/**
 * @param {string} haystack
 * @param {string} needle
 * @return {number}
 */
var strStr = function(haystack, needle) {
    if (needle === '') {
        return 0;
    } else {
        var i = 0;
        for (; i < haystack.length; i++) {
            var re = new RegExp('^' + needle);
            if(re.test(haystack.substring(i))) {
                return i;
            }
        }
        return -1;
    }
};